1. Field of the Invention
The present invention relates generally to a longitudinal acceleration sensor, and more particularly, to a device for calibrating a longitudinal acceleration sensor of a vehicle.
2. Description of the Prior Art
The longitudinal acceleration sensor is one of the essential sensors of the modern vehicles incorporating the so-called vehicle stability control which automatically controls running behaviors of the vehicles for higher performances and stability thereof based upon calculations of vehicle dynamics made available by the developments of micro-computers. In order to ensure the actual effectiveness of those vehicle stability controls, it is very important that the longitudinal acceleration sensors are correctly calibrated, particularly with respect to the neutral point thereof.
Since the longitudinal acceleration sensor generally incorporates a pendulum responsive to the gravitational force of the earth, while the grounds where the vehicles are stopped or parked are not always correctly horizontal, it is not generally possible to calibrate the neutral point of the longitudinal acceleration sensor in such a static manner as to measure a shifting of the natural stop position of the pendulum from a geometrically neutral position of the longitudinal acceleration sensor.
In Japanese Utility Model Publication 7-17525 filed by the assignee company of the present application together with a co-applicant, it has been proposed to calibrate a longitudinal acceleration sensor of a vehicle by calculating a mean value of the output of the longitudinal acceleration sensor through a period of running of the vehicle, and then comparing the mean value with the output value of the longitudinal acceleration sensor during a stoppage of the vehicle, so as to presume that, when the both are substantially equal to one another, the vehicle is stopped on a horizontal base, thereby presuming said output value as a shifting of the neutral point of the longitudinal acceleration sensor.
The above prior art will provide a good calibration of the longitudinal acceleration sensor when the calibration is made by using data collected over a relatively long period of running of the vehicle such that the deflections of the output of the sensor due to sloping up runnings of the vehicle are naturally canceled by those due to sloping down runnings of the vehicle in a certain stable daily driving area.